Probes with offset arm and suspension structure

ABSTRACT

A probe having a conductive body and a contacting tip that is terminated by one or more blunt skates for engaging a conductive pad of a device under test (DUT) for performing electrical testing. The contacting tip has a certain width and the blunt skate is narrower than the tip width. The skate is aligned along a scrub direction and also has a certain curvature along the scrub direction such that it may undergo both a scrub motion and a self-cleaning rotation upon application of a contact force between the skate and the conductive pad. While the scrub motion clears oxide from the pad to establish electrical contact, the rotation removes debris from the skate and thus preserves a low contact resistance between the skate and the pad. The use of probes with one or more blunt skates and methods of using such self-cleaning probes are especially advantageous when testing DUTs with low-K conductive pads or other mechanically fragile pads that tend to be damaged by large contact force concentration.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 11/480,302, entitled “Probes with Self CleaningBlunt Skates for Contacting Conductive Pads”, to January Kister, filedon Jun. 29, 2006, which claims priority to and the benefit of U.S.patent application Ser. No. 10/888,347 (now U.S. Pat. No. 7,091,729),entitled “Cantilever Prove with Dual Plane Fixture and Probe Apparatus”,to January Kister, filed on Jul. 9, 2004, and the specifications andclaims thereof are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to cantilever probes. In particular, thepresent invention relates to a cantilever probe with angle fixture and aprobe apparatus therewith. The present invention relates generally toprobes for testing devices under test (DUTs), and in particular toprobes with contacting tips terminated in blunt skates to promoteself-cleaning on contact with contacting pads as well as self-cleaningmethods.

BACKGROUND ART

Continuing miniaturization of cantilever probes imposes new challengesfor their positioning and fixing within a probe apparatus. Cantileverprobes are commonly fixed with their peripheral ends having theircantilever portion with the contacting tip freely suspended to providethe required flexibility. To provide sufficient positioning accuracy,the fixture portion of the cantilever probe is commonly extensivelydimensioned, which in turn consumes extensive real estate forcingmultilayer cantilever probe assemblies with varying cantilevergeometries. Such varying cantilever geometries result in differentdeflection behavior and limited average positioning accuracy of allcantilever probes of a probe apparatus. In addition, cantilever probesof the prior art are commonly fixed in a surrounding fashion along alinear fixture element, which requires additional surroundingreferencing and/or positioning structures, which in turn consumeadditional space between the cantilever probes.

Prior art cantilever probes are commonly fabricated with lengthyperipheral structures for a sufficient fanning out between the everdecreasing test contact pitches and circuit board contacts of the probeapparatus. Peripheral fan-out structures may be a multitude of thecantilever portion, which reduces the positioning accuracy of the everdecreasing cantilevers and contacting tips.

For the reasons stated above, there exists a need for a cantilever probeand probe assembly that provides maximum contacting tip accuracytogether with homogeneous deflection behavior within a minimumfootprint. In addition, cantilever probes may be simple and highlyconsistent in geometry for inexpensive mass production. Other affiliatedstructures of the probe apparatus may be inexpensively fabricated toaccommodate for highly individualized probe apparatus configurations.Embodiments of the present invention address these needs.

The testing of semiconductor wafers and other types of integratedcircuits (ICs), collectively known as devices under test (DUTs), needsto keep pace with technological advances. Each IC has to be individuallytested, typically before dicing, in order to ensure that it isfunctioning properly. The demand for testing products is driven by twoconsiderations: new chip designs and higher volumes. As chips becomeincreasingly powerful and complicated, the need for high-speed probecard devices to test them becomes more and more deeply felt.

In particular, chips are getting smaller and they have more tightlyspaced conductive pads. The pads are no longer located about the circuitperimeter, but in some designs may be found within the area occupied bythe circuit itself. As a result, the density of leads carrying testsignals to the pads is increasing. The pads themselves are gettingthinner and more susceptible to damage during a test. Meanwhile, theneed to establish reliable electrical contact with each of the padsremains.

A well-known prior art solution to establishing reliable electricalcontact between a probe and a pad of a DUT involves the use of probesthat execute a scrub motion on the pad. The scrub motion removes theaccumulated oxide layer and any dirt or debris that acts as an insulatorand thus reduces contact resistance between the probe and the pad. Forinformation about corresponding probe designs and scrub motion mechanicsthe reader is referred to U.S. Pat. No. 5,436,571 to Karasawa; U.S. Pat.Nos. 5,773,987 and 6,433,571 both to Montoya; U.S. Pat. No. 5,932,323 toThrossel and U.S. Appl. 2006/0082380 to Tanioka et al. Additionalinformation about the probe-oxide-semiconductor interface is found inU.S. Pat. No. 5,767,691 to Verkuil.

In order to better control the scrub motion, it is possible to vary thegeometry of the contacting tip of the probe. For example, the radius ofcurvature of the tip may be adjusted. In fact, several different radiiof curvature can be used at different positions along the probe tip. Foradditional information about probe tips with variable radii of curvaturethe reader is referred to U.S. Pat. No. 6,633,176 and U.S. Appl.2005/0189955 both to Takemoto et al.

Although the above-discussed prior art apparatus and methods provide anumber of solutions, their applications when testing conductive padsthat are thin or prone to mechanical damage due to, e.g., theirthickness or softness is limited. For example, the above probes andscrub methods are not effective when testing DUTs with low-K conductivepads made of aluminum because such pads are especially prone to damageby probes with tips that either cut through the aluminum or introducelocalized stress that causes fractures. In fact, a prior art solutionpresented in U.S. Pat. No. 6,842,023 to Yoshida et al. employs contactprobe whose tip tapers to a sloping blade or chisel. The use of thistype of probe causes a knife edge and/or single point of contact effectsto take place at the tip-pad interface. These effects can causesirreversible damage to pads, especially low-K conductive pads made ofaluminum or soft metal. On the other hand, when insufficient contactforce is applied between the probe tip and the pad, then the oxide andany debris at the probe-pad interface will not be efficiently removed.

The problem of establishing reliable electrical contact with fragileconductive pads remains. It would be an advance in the art to provideare probes that can execute effective scrubbing motion and areself-cleaning, while at the same time they do not cause high stressconcentration in the pad. Such probes need to be adapted to probe cardsfor testing densely spaced pads.

OBJECTS AND ADVANTAGES

In view of the above prior art limitations, it is an object of theinvention to provide probes that are self-cleaning upon contact andavoid long-term accumulation of debris to thus preserve their ability toestablish good electrical contact or low contact resistance R_(c).

It is a further object of the invention to provide probes that reducemechanical stress concentration in the pads of the DUT being tested torender the probes suitable for testing low-K conductive pads.

A still further object of the invention is to provide probes andself-cleaning methods that can be applied in various probe geometries,probe cards and test arrangements.

These and other objects and advantages of the invention will becomeapparent from the ensuing description.

SUMMARY OF THE INVENTION

A cantilever probe has an elbow for bonding to a dual plane fixtureplate having two substantially non parallel fixture surfaces in an anglecorresponding to the elbow. The dual plane angled fixture between elbowand fixture plate provides for a highly stiff and precise hold of thebonded cantilever probe with minimal real estate consumption. Thecantilever probe may feature at least two positioning pins one of whichmay be placed at the contacting tip and the other one may extend from atleast one of two contacting faces of the elbow. The elbow positioningpin may fit into a corresponding elbow pin hole on one of the fixturesurfaces. The tip positioning pin may fit into a corresponding tip pinhole of a sacrificial assembly plate temporarily combined with thefixture plate for a precise positioning of the cantilever probes duringcuring, setting or hardening of a bonding agent between the fixtureplate an the elbow. After assembly of a number of cantilever probes, thesacrificial plate may be removed and the tip pins eventually sanded to acommon plane.

Separate fan-out beams may be aligned with beam positioning pins on andattached to the fixture plate. The fan-out beams are aligned andconductively connected with their probe connect ends to respective probeelbows once the cantilever probes are fixed. The fan-out beams in turnmay be conductively connected with their respective peripheral connectends to well known large pitch apparatus terminals of a circuit board.Cantilever probes and fan-out beams may have geometries suitable forinexpensive mass fabrication by well known masked electro depositionfabrication techniques. A probe apparatus may be easily customized byproviding varying drill patterns of the positioning holes for fan-outbeams and cantilever probes to match pitch requirements of the testedcircuit chips.

The objects and advantages of the invention are secured by a probedesigned for engaging a conductive pad of a device under test (DUT). Theprobe has an electrically conductive body that ends in a contacting tipof a certain tip width. At least one blunt skate that is narrower thanthe tip width terminates the contacting tip. The blunt skate is alignedalong a scrub direction and also has a certain curvature along the scrubdirection to produce a self-cleaning rotation or rocking motion. As aresult of the alignment and skate geometry, once a contact force isapplied between the blunt skate and the conductive pad the skateundergoes a scrub motion along the scrub direction and also aself-cleaning rotation. While the scrub motion clears oxide from the padto establish electrical contact, the rotation removes debris from theskate and thus preserves low contact resistance between the skate andthe pad.

To promote the self-cleaning rotation the curvature of the blunt skateneeds to have an appropriate radius of curvature. Preferably, the radiusof curvature is variable and decreasing towards the front of the skate.Since the skate is preferably symmetric about a midpoint, the samevariable radius of curvature can be used in the back half of the skate.In one embodiment the cross-section of the blunt skate is flat and inanother it has a rounded cross-section. In general, it is preferablethat the skate have a width of less than 12 μm and a length of less than75 μm. It should be noted that probes with blunt skates in thisdimensional range are very well-suited for contacting DUTs with low-Kconductive pads that are mechanically fragile.

In some embodiments the probe is made of material layers. Such layerscan be grown, e.g., in a deposition process. In these embodiments theblunt skate can be formed from an extension of one of the materiallayers. The most appropriate material layer for forming a blunt skatefrom its extension is a hard conductive material such as rhodium orcobalt. In either the layered probe embodiments or still otherembodiments it is possible to provide two or more blunt skates. Theskates can be arranged parallel to each other. Alternatively, or inaddition the skates can be staggered along the scrub direction.

The invention further extends to a method for engaging probes that haveconductive bodies and contacting tips terminating in one or more bluntskates with a conductive pad. The skate or skates are narrower than thetip width. The skate or skates are provided with a curvature alignedalong the scrub direction for producing the self-cleaning rotation. Theapplication of a contact force between the skate and the conductive padcauses the skate to undergo a scrub motion along the scrub direction anda self-cleaning rotation that removes debris. The debris is usuallyaccumulated during previous engagements with or touch-downs on pads andits removal from the skate preserves low contact resistance.

In accordance with a preferred embodiment of the method, the contactforce is augmented to increase the self-cleaning rotation. This can bedone whenever excess debris accumulates. Typically this will take placeafter several cycles, and thus the contact force can be augmented aftertwo or more touch-down cycles to augment the self-cleaning rotation.

To perform a test, a test current i is applied to the probe afterapplying the contact force. This means that the skate delivers the testcurrent i to the pad after performing the scrub motion that removes anyoxide from the pad and establishing electrical contact with it. Notethat no current is applied when performing increased self-cleaningrotation of the skate. The same method is applied when two or moreparallel and/or staggered skates are used.

The probes of invention can be used in various apparatus and situations.For example, the probes can be used in a probe card for testing devicesunder test (DUTs) such as semiconductor wafers. The probe card requiresappropriate design and devices, such as a source for delivering the testcurrent i as well as arrangements for providing the overdrive to applythe contact force between the probes and the pads of the DUT.

A detailed description of the preferred embodiments of the invention ispresented below in reference to the appended drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1A is a front view of an exemplary cantilever probe of thepreferred embodiment parallel a symmetry plane of the cantilever probe.

FIG. 1B is a perspective view of the cantilever probe of FIG. 1A.

FIG. 2 is the perspective view of a first portion of a fixture plateincluding two fixture surfaces and elbow alignment holes.

FIG. 3 is the perspective view of the fixture plate of FIG. 2 togetherwith a sacrificial spacing structure and sacrificial assembly plate.

FIG. 4 is the perspective view of the plates of FIG. 3 with a number ofassembled cantilever probes of FIGS. 1A, 1B.

FIG. 5 is the perspective view of assembled probes and fixture plate ofFIG. 4 with removed sacrificial spacing structure and sacrificialassembly plate.

FIG. 6 is the perspective view of a second portion of a fixture plateincluding the first portion of FIG. 2 and alignment holes for fan-outbeams.

FIG. 7 is the perspective view of an exemplary fan-out beam.

FIG. 8 is the perspective view of the assembled cantilever probes andfixture plate of FIG. 5, the fixture plate of FIG. 6 and a number ofassembled fan-out beams of FIG. 7 conductively connected with respectivecantilever probes.

FIG. 9 is a three-dimensional view of a portion of a probe cardemploying probes with blunt skates according to the invention.

FIG. 10A is a plan side view of a contacting tip of a single probe fromFIG. 9 equipped with a blunt skate.

FIG. 10B is a front cross-sectional view of the contacting tip of thesingle probe from FIG. 9.

FIG. 11A-D are three-dimensional views of the successive steps inengaging a blunt skate with a low-K conductive pad.

FIG. 12 (prior art) is a graph of contact resistance R_(c) between atypical flat contacting tip and a conductive pad as a function oftouch-down cycles.

FIG. 13 is a graph of contact resistance R_(c) between a contacting tipequipped with a blunt skate in accordance with the invention and aconductive pad.

FIG. 14 is a diagram comparing the performance of a prior art chisel tipand a tip with a blunt skate in accordance with the invention.

FIG. 15A-D are three-dimensional views of alternative probe tips withone or more blunt skates according to the invention.

FIG. 16A-B are microscope images of a preferred blunt skate prior to useand after one million touch-down cycles.

DETAILED DESCRIPTION

Referring to FIGS. 1A, 1B, a cantilever probe 1 for test contacting awell known test contact of a tested electronic circuitry along acontacting axis CA may have a tip positioning pin 14 configured for thetest contacting. The tip positioning pin 14 may also be configured foran aligning insertion in a respective one of tip pin holes 43A-43N (seeFIG. 3) also along the contacting axis CA. The cantilever probe 1 mayfurther feature a cantilever 13 for resiliently holding the tippositioning pin 14 with respect to the contacting axis CA with apredetermined deflection behavior including a well known scrub motionalong the symmetry plane SP.

A base arm 11 may rigidly extend from said cantilever probe 13 such thatoperational deflection of the cantilever 13 leaves a base arm assemblyface 111 substantially free of deformation. An offset arm 12 extendssubstantially rigid from the base arm 11 in a substantially non parallelelbow angle AE defining together with the base arm 11 a fixture elbow 10for rigidly fixing the cantilever probe 1 preferably via base armassembly face 111 and offset arm assembly face 122. An elbow positioningpin 15 extends from one of the base arm 11 and the offset arm 12 alongan elbow pin axis PA, which is substantially parallel to the contactingaxis CA. The elbow positioning pin 15 is configured for an aligninginsertion in a respective one of elbow pin holes 23A-23N (see FIGS. 2,6) together with aligning insertion of the tip positioning pin 14. Thebase arm assembly face 111 has a length 111L and the offset arm assemblyface 121 has length 121L. The contacting axis CA is in a probe pindistance AP to the elbow pin axis PA.

The cantilever 13 may preferably have a bend 131 terminating at the basearm 11, which in turn may preferably extend substantially parallel tothe contacting axis CA. In that case, the elbow positioning pin 14 mayextend from the offset arm 12.

The cantilever 13, the base arm 11 and the offset arm 12 may have acontinuously protruding profile perpendicular with respect to thesymmetry plane SP and the contacting axis CA. In such case, thecantilever probe 1 may be fabricated by a masked electro depositionprocess in which a central layer including the position pins 14, 15 isinterposed between profile layers. As a result, the positioning tips 14,15 may have at least rectangular but preferably square cross section.The cantilever probe 1 may consequently be also substantially symmetricwith respect to the symmetry plane SP that coincides with the contactingaxis CA and the elbow pin axis PA.

Deflection behavior of the cantilever 13 may be tuned by adjusting thecantilever length 13L, cantilever height 13H, profile width 1W as wellas shape and material composition of the cantilever 13 as may be wellappreciated by anyone skilled in the art. Furthermore, instead of thecantilever 13 another suspension structure may be employed such as asuspension knee disclosed in the cross referenced US application, titled“Freely Deflecting Knee Probe With Controlled Scrub Motion”. Thereby,the tip positioning pin may be combined with the suspension knee at thecontacting face.

Referring to FIG. 2, a probe fixture plate 2 for fixedly holding anumber of cantilever probes 1 may have a first fixture surface 22featuring a number of primary positioning holes 23A-23N for the alignedinsertion of a number of elbow positioning pins 15. The probe fixtureplate 2 may additionally feature a second fixture surface 21 in asubstantially non parallel fixture surface angle SA to said firstfixture surface 22. The fixture surface angle SA corresponds to theelbow angle AE. The second fixture surface 22 preferably extends insubstantially constant offset 23O to an array direction of thepositioning holes 23A-23N arrayed with positioning hole pitch 23P.

In case the primary elbow positioning holes 23A-23N are linearlyarrayed, the second fixture surface 21 may be planar. The fixturesurface angle SA may be perpendicular.

Referring to FIG. 3, a temporary plate assembly 100 may include asacrificial assembly plate 4 separable attached to an attachment face 24of the probe fixture plate 2. The sacrificial assembly plate 4 has athird surface 42 with secondary tip positioning holes 43A-43N in a probepositioning hole offset AL that corresponds to the probe pin distanceAP. A secondary hole pitch 43P may be preferably equal or less than theprimary hole pitch 23P. The attachment face 24 may be opposite the firstfixture surface 22.

The third surface 42 may be in a surface offset 40H to the first fixturesurface 22 in direction of the primary holes 23A-23N and secondary holes43A-43N. In the case where the surface offset 40H is substantiallylarger than a fixture plate height 20H, a sacrificial spacing structure3 may be interposed between the probe fixture plate 2 and thesacrificial assembly plate 2. Sacrificial assembly plate 4 andsacrificial spacing structure 3 may be separable by use of a selectivelydissolvable solder or other bonding agent as may be well appreciated byanyone skilled in the art.

Referring to FIG. 4, a probe bonding assembly 101 may include thetemporary plate assembly 100 and a number of cantilever probes 1A-1Naligned inserted with their elbow positioning pins 15 in a respectiveone of the elbow positioning holes 23A-23N and their tip positioningpins 14 concurrently aligned inserted in a respective one of the tippositioning holes 43A-43N. As a result, the base arm assembly face 111may be brought into a combining proximity with the second fixturesurface 21 and the offset arm assembly face 121 may be brought into acombining proximity with the first fixture surface 22. For that purpose,the elbow pin axis PA may be in an assembly face offset PO to theadjacent assembly face that is equal or slightly larger the constantoffset 23O between the center of the elbow positioning holes 23A-23N andthe second fixture surface 21. In case of the cantilever probe 1 theassembly face offset PO is between offset arm assembly face 121 and theelbow positioning pin 15.

A robotic probe assembling may be accomplished in combination with avacuum fixture holding a cantilever probe 1 and moving it towardsassembly position in direction along the contacting axis CA and elbowpin axis PA. In cases where the scale of the positioning pins 14, 15 isclose to the positioning accuracy of the robotic assembly system, asequential aligned insertion may be accomplished by varying the elbowpin height 15H from the tip pin height 14H. Once a first alignedinsertion is accomplished, the second aligned insertion may be attemptedwithout risk of again misaligning the other of the positioning pins 14,15.

Referring to FIG. 5, a fixed probe assembly 102 features a number ofcantilever probes 1A-1N fixed with their respective fixture elbows10A-10N to the fixture plate 2 preferably by applying a combining orbonding agent in the combining proximity between the assembly faces 111,121 and their respective fixture surfaces 21, 22. A combining or bondingagent may be for example an epoxy or a solder. In case a solder is used,an electrically conductive connection may be simultaneously establishedbetween the fixture elbows 10A-10N and eventual conductive traces on oneor both of the fixture surfaces 21, 22. Sacrificial assembly plate 4 andeventual sacrificial spacing structure 3 are removed. The tippositioning pins 14A-14N are configured to operate additionally for testcontacting along their respective contacting axis CAA-CAN with aneventual scrub motion. For that purpose, the tip positioning pins14A-14N may be adjusted to a common tip clearance 1H by a sandingoperation.

The contacting axes CAA-CAN are in a contacting pitch 1P thatcorresponds to the secondary hole pitch 43P. In case of linear arrayedelbow positioning holes 23A-23N and planar second fixture surface 21,the cantilever probes 1 may be parallel assembled with constant gap 1Gand constant profile width 1W.

The elbow positioning holes 23A-23N may also be arrayed with curvatureand the second fixture surface 21 may be concentric as well as thesecondary positioning holes 43A-43N being concentrically arrayed withproportionally reduced secondary hole pitch 43P. In that case, thecantilever probes 1 may be arrayed with minimal contacting pitch 1.Furthermore, the probes 1 may have a proportionally decreasing profilewidth 1 resulting again in a constant probe spacing 1G. Anotheradvantage may be a favorably balanced stress distribution as a result ofthe profile width 1 increasing proportionally with the distance from thecontacting axes CAA-CAN, which corresponds to the bending stressincreasing in the cantilever 13 away from the contacting axes CAA-CAN asmay be well appreciated by anyone skilled in the art.

The angled fixture is particularly advantageous in minimizing an overallreal estate of the fixed probe assembly in perpendicular extension tothe contacting axes CAA-CAN. This results on one hand from utilizing thesecond fixture surface 21 preferably parallel to the contacting axesCAA-CAN, which consumes only a minimal real estate independently of thefixture plate height 20H. The minimized overall real estate results onthe other hand from an increased stiffness and thermal stability of theangled fixture due to the three dimensional configuration of the bondinginterface between fixture surfaces 22, 21 and the assembly faces 121,111 together with a reduced combining proximity and minimal use ofcombining agent. Further more, the bonding interface is free of lateralstructures in between adjacent cantilever probes 1, resulting in amaximum profile width 1, which in turn assists in designing suspensionstructures highly resistant against inadvertent deviating torsionbending.

Referring to FIG. 6, the first fixture surface 22 may further featurealignment holes 25A-25N and orienting holes 26A-26N. Each of thealignment holes 25A-25N defines with a respective one of the orientingholes 26A-26N one of the positioning axes 27A-27N. The positioning axes27A-27N may be oriented in a fan-out angle AF with respect to anadjacent one of the positioning axes 27A-27N. Consequently, an alignmenthole distance DA between adjacent ones of the alignment holes 25A-25N issubstantially smaller than an orienting hole distance DO betweenadjacent ones of the orienting holes 26A-26N. The alignment holedistance DA is about the same as the positioning hole pitch 23P. Thedistance of the positioning axes 27A-27N corresponds to a beam pindistance 57 (see FIG. 7).

Particular advantageous is a fabrication step of concurrently drillingall holes 23A-23N, 43A-43N, 25A-25N and 26A-26N without need ofintermediate repositioning of the temporary plate assembly 100, whichprovides for highest hole position accuracies with minimal machiningeffort. In that way highly individualized probe assemblies may befabricated in combination with standardized cantilever probes 1 andfan-out beams 5 (see FIG. 7).

Referring to FIG. 7, a fan-out beam 5 may be fabricated fromelectrically conductive material with a beam length 51L. The fan-outbeam 5 may have a probe connect end 52 and a peripheral connect end 53on a connect surface 51. Opposite the connect surface 51 may be a beamattachment face 56 featuring an elbow alignment pin in the proximity ofthe probe connect end 52. A fan-out orienting pin 55 may be with itsorienting pin axis 55C in a beam pin distance 57 to alignment pin axis54C. The fan-out beam 5 may be fabricated similarly like the cantileverprobe 1 with a masked electro deposition process in a multi layerfashion.

Referring to FIG. 8, a probe and fan-out beam assembly 103 features afixed probe assembly 102 with the fixture plate 2 of FIG. 6 with respectto which a number of fan-out beams 5A-5C are positioned via their elbowalignment pins 54 in respective ones of the alignment pin holes 25A-25Nand oriented with their orienting pins 55 in respective ones of theorienting pin holes 26A-26N such that their probe connect ends 52A-52Nare in close proximity to respective ones of elbow fixtures 10A-10N. Thefan-out beams 5 may be bonded or combined with its attachment face 56with the first fixture surface 22.

Conductive bridges 6A-6N electrically conductive connect fixture elbows10A-10N with respective ones of the probe connect ends 52A-52N such thata solid conductive path is established between the tip positioning pins14A-14N and respective ones of the peripheral connect ends 53A-53N. Theconductive bridges 6A-6N may be fabricated by well known wire bondingand/or wedge bonding techniques.

The fan-out beams 5 may be alternately lengthened for a zigzag connectend pattern for increased spacing between adjacent ones of theperipheral connect ends 53A-53N, which may be conductively connected towell known assembly contacts of a probe apparatus.

Fixed probe assembly 102 and/or probe and fan-out beam assembly 103 maybe part of a probe apparatus for testing electronic circuitry. Fan-outbeams 5 and probes 1 may be economically fabricated in large number in acommon configuration and combined with individually fabricated fixtureplates 2.

A portion of a probe card assembly 900 employing probes 902 according tothe invention is shown in FIG. 9. Assembly 900 has a block 904 forholding probes 902 by their contact ends 906. A space transformer,electro-mechanical arrangements as well as a source for providing a testcurrent i to be applied to contact ends 906 are not shown in thisdrawing for reasons of clarity.

Probes 902 have electrically conductive bodies 908 that end incontacting tips 910 of a tip width 912. Bodies 908 have suitablemechanical properties for engaging with conductive pads or bumps of adevice under test (DUT). For example, bodies 908 can be straight, bentor have more complex geometries to ensure sufficient mechanical strengthand compliance, as will be appreciated by those skilled in the art. Infact, although probes 902 have bodies 908 that are bent in the presentembodiment, the invention can be practiced with probes of any geometry.

Tips 910 terminate in blunt skates 914 that are narrower than tip width912. In fact, skate width 916 is typically a fraction of tip width 912.For example, tip width 912 can be on the order of 75 μm while skatewidth 916 is about 12 μm or less. Skates 914 are aligned along a scrubdirection 920 indicated by an arrow.

As better shown in the plan side view of FIG. 10A, each blunt skate 914has a certain curvature along scrub direction 920. In other words, theridge of skate 914 that is aligned with scrub direction 920 has acertain curvature along that direction. The curvature is defined in sucha way as to produce a self-cleaning rotation sometimes also referred toas pivoting or rocking motion of skate 914. In the present embodiment,the curvature has a variable radius of curvature R that decreases towarda front 922 of skate 914. More specifically, the radius of curvature hasa small value R_(m) at front 922 and a larger value R_(n) near thecenter of skate 914.

Skate 914 in the present embodiment is symmetric about a center line 924that passes through a midpoint 926 of skate 914. Therefore, the samevariable radius of curvature is found in the back half of skate 914. Itis important that the curvature at every point along skate 914 that willengage with a pad is sufficiently large to avoid single point of contactor knife edge effects. These effects cause large amounts of local stressto develop in the pad and in the case of low-K pads can cause damage.Such effects are especially likely to develop along skate 914 at frontand back regions, such as region 928 indicated in hatching. To furtherhelp avoid these effects, the cross-section of skate 914 has a roundedrather than a flat cross section, as better visualized in the frontcross-sectional view of FIG. 10B.

The operation of probes 902 will be explained in reference to thethree-dimensional views shown in FIGS. 11A-D. In FIG. 11A contacting tip910 with blunt skate 914 is positioned above a conductive pad 930 of adevice under test (DUT) 932. Only a portion of DUT 932 is shown forclarity. In this position, no test current i is applied (i=0) to probe902.

It is understood that DUT 932 can be any device that requires electricaltesting including, for example, a semiconductor wafer bearing integratedcircuits. Also, it is understood that pad 930 can have any geometry andcan also be in the form of a solder bump or any other form suitable forestablishing electrical contact. In the present embodiment pad 930 is alow-K conductive pad.

In FIG. 11B a contact force F_(c) is applied between blunt skate 914 andlow-K conductive pad 930. This force can be delivered by any suitablemechanism well-known to an artisan skilled in the art. At this time,there is still no test current applied (i=0).

FIG. 11C illustrates how tip 910 pivots and skate 914 performs a scrubmotion along scrub direction 920. The scrub motion is caused by a scrubforce F_(s1) that is due to contact force F_(c). The purpose of scrubmotion of skate 914 is to clear oxide from pad 930 to establishelectrical contact between skate 914 and pad 930. The alignment of skate914 with scrub direction 920 and the geometry of skate 914, namely itscurvature causes the scrub motion to be accompanied by a self-cleaningrotation or pivoting of skate 914.

The self-cleaning rotation removes debris 934 that is accumulated onskate 914 or that is originally located on pad 930 from skate 914.Typically, debris 934 accumulates on skate 914 during previousengagements with or touch-downs on pads. The self-cleaning rotationpushes debris 934 to the back and off the sides of skate 914. Removal ofdebris 934 from the skate-pad interface enables a low contact resistanceR_(c) to be preserved between skate 914 and pad 930. Once such lowcontact resistance R_(c) has been established, a test current i=i_(o) isapplied to pad 930.

FIG. 11D shows the effects of augmenting contact force F_(c) to furtherincrease the self-cleaning rotation of skate 914. This can be donewhenever excess of debris 934 accumulates on skate 914. In a preferredembodiment of the method of invention, contact force F_(c) is augmentedafter a certain number of touch-down cycles or whenever the contactresistance is observed to reach unacceptable levels. This may occurafter two or more touch-down cycles or when resuming testing after along stand-by period. Note that the resultant scrub force F_(s2) islarger as a result of the increased contact force F_(c) and that no testcurrent (i=0) is applied during this procedure.

A graph 940 in FIG. 12 shows the contact resistance R_(c) between atypical flat prior art contacting tip and a conductive pad as a functionof touch-down cycles. Clearly, contact resistance R_(o) increases from anominal value R_(o) of about 1μ as a function of cycles n. The slope ofthe increase grows as a function of n until reaching a maximumresistance R_(max). Testing the pads becomes impossible once contactresistance R_(c) reaches R_(max). At this point, the prior art tips aresanded down to remove debris and recover nominal contact resistanceR_(o). This corresponds to the dashed portion 942 of graph 940.Unfortunately, sanding down accelerates the accumulation of debris onthe tip. This causes the slope of contact resistance increase to becomesteeper and reach the unacceptably high value R_(max) even sooner.Another sanding denoted by dashed portion 944 is required to againrecover nominal resistance R_(o).

FIG. 13 shows an exemplary graph 950 of contact resistance R_(c) betweencontacting tip 910 with blunt skate 914 in accordance with the inventionand a conductive pad. As contact resistance R_(c) increases from nominalvalue R_(o), the self-cleaning rotation of skate 914 tends to restore itto R_(o). In some cases no additional intervention is necessary. IfR_(c) does begin to grow too much and an immediate decrease of contactresistance R_(c) is desired, then the contact force F_(c) is augmentedto increase the self-cleaning rotation of skate 914. Portions 952 ofgraph 950 visualize the corresponding reductions of contact resistanceR_(c) to nominal value R_(o).

FIG. 14 shows a comparison in the concentration of mechanical stresscaused in low-K conductive pad 930 by a prior art chisel probe tip 960and a blunt skate 962 with a flat cross-section in accordance with thepresent invention. Pad 930 is made of aluminum and both tip 960 andskate 962 are made of Rhodium. Chisel probe tip 960 has a 60 degreetaper angle, a 2 mil radius at its contact tip and is 60 μm long. Skate962 is 10 μm wide, its ends are rounded with a 10 mil radius ofcurvature and it is also 60 μm long. The contact force F_(c) applied ineach case is 8 g. The stress caused by prior art chisel probe tip 960 isvery large and concentrated in the middle of pad 930. This causesmechanical failure of pad 930 by fracture. In contrast, the stress iswell-distributed when blunt skate 914 according to the invention is usedto establish electrical contact with pad 930.

Various types of probes can employ blunt skates according to theinvention, as illustrated in FIGS. 15A-D. In some embodiments a probe1500 is made of several material layers 1502, 1504, 1506, as illustratedin FIG. 15A. Such layers can be grown, e.g., in a deposition process. Inthese embodiments a blunt skate 1508 can be formed at a tip 1510 from anextension of one of the material layers. In the embodiment shown, it isthe extension of the central or sandwiched material layer 1504 thatforms skate 1508. The most appropriate material layer for forming ablunt skate from its extension is a hard conductive material such asrhodium or cobalt. In fact, material layer 1504 is made of rhodium inthe present embodiment. In alternative probes having more layersextensions of other than central layers can be used. In fact, even theouter-most layers may be extended to form blunt skates according to theinvention.

FIG. 15B illustrates a probe 1520 with a laser machined blunt skate1522. For example, skate 1522 has a higher aspect ratio than previousskates and also a single radius of curvature. Such geometry can beemployed when relatively short scrub motion is imposed by a higher pitchof conductive pads. In fact, the curvature of skate 1522 can be adjustedin concert with the characteristics of the scrub motion as conditionedby the geometry of the probe. These characteristics may include, amongother, scrub length, scrub depth and scrub velocity.

In either the layered probe embodiments or still other embodiments it ispossible to provide two or more blunt skates, as illustrated by probe1530 of FIG. 15C. Probe 1530 is made of three material layers 1532,1534, 1536 and of those the side layers 1532, 1536 are extended to formblunt skates 1538, 1540. Skates 1538, 1540 are arranged parallel to eachother and along the scrub direction. Of course, more than two skates1538, 1540 can be accommodated on the tip of a probe when more materiallayers are available.

Still another alternative embodiment is shown in FIG. 15D. Probe 1550shown here has five material layers 1552, 1554, 1556, 1558 and 1560 withlayers 1552, 1556 and 1560 being extended. Three blunt skates 1562,1564, 1566 are formed from extensions of layers 1552, 1556, 1560. Theseskates are also parallel to each other, but in addition they arestaggered along the scrub direction.

A person skilled in the art will appreciate that various othercombinations of skates are possible. In addition, the blunt skates canbe employed at the tips of various types of probes, including probesthat are linear or bent. For example, zig-zag probes, S-shaped probes orprobes with a knee can employ one or more blunt skates each to improvecontact resistance with the pads of the DUTs. Also, when equipped withthe blunt skates of the invention, these probes can be used to contactmore fragile conductive pads, e.g., very thin pads or pads that userelatively soft metals.

FIGS. 16A-B are microscope images of a preferred embodiment of a bluntskate that has a rounded cross-section, similar to the skate describedin FIGS. 10A-B. FIG. 16A shows the skate prior to use and FIG. 16B showsit after one million touch-down cycles. The skate has a width of about10 μm and a length of 200 μm. Note how the skate is free of debris evenafter the one million touch-down cycles. In fact, the debris has atendency to be pushed off to the sides of the skate and attach tonon-critical portions of the probe tip.

The probe card requires appropriate design and devices, such as a sourcefor delivering the test current i as well as arrangements for providingthe overdrive to apply the contact force between the probes and the padsof the DUT. The design of probe cards as well as the aforementioneddevices are well-known to those skilled in the art. It will beappreciated by those skilled artisans that probes equipped with bluntskates in according to the invention can be employed in probe cards ofvarious designs, including probe cards with and without spacetransformers. The probes themselves can be removable in embodiments thatuse space transformers or they can be permanently attached usingsoldering techniques or mechanical locking such as press fit into aconductive via.

The probes of invention are thus very versatile and are able toestablish reliable electrical contact with even densely spaced fragileconductive pads or low-K pads. The pads can be arranged in accordancewith various geometries, including dense arrays. They are able to dothat because the combined scrub motion and self-cleaning rotation of theblunt skate does not cause a high stress concentration in the pad. Dueto the large number of possible variations and types of probes thatemploy blunt skates, the scope of the invention should be judged by theappended claims and their legal equivalents.

1. A probe assembly for testing a device under test comprising: afixture plate for holding a plurality of probes, said fixture platecomprising: a first fixture surface comprising a primary positioninghole arrayed with a positioning hole pitch; a second fixture surface ina substantially non-parallel fixture surface angle to said first fixturesurface; said at least one of said plurality of probes disposed on saidfixture plate, said probe comprising: an offset arm extending outwardlyin a first direction; a suspension structure comprising one end at saidoffset arm and an opposing tip end, said opposing tip end comprising atip positioning pin; said suspension structure extending downwardly fromsaid offset arm in a second direction; and said suspension structurefurther extending outwardly at said tip end in substantially said firstdirection.
 2. The probe assembly of claim 1 wherein said probe furthercomprises an elbow between said offset arm and said suspensionstructure.
 3. The probe assembly of claim 1 wherein said tip positioningpin is configured for insertion in a tip pin hole along a contactingaxis.
 4. The probe assembly of claim 1 wherein said tip positioning pincomprises a rectangular cross section.
 5. The probe assembly of claim 1wherein said tip positioning pin comprises a square cross section. 6.The probe assembly of claim 1 wherein said probe further comprises anelbow positioning pin extending from said offset arm.
 7. The probeassembly of claim 1 wherein said probe comprises a center layercomprising said tip positioning pin interposed between outer layers. 8.The probe assembly of claim 6 wherein said elbow positioning pin isdisposed in said primary positioning hole.
 9. The probe assembly ofclaim 1 further comprising a sacrificial assembly plate separablyattached to an attachment face of said fixture plate.
 10. The probeassembly of claim 9 further comprising a sacrificial spacing structureinterposed between said probe fixture plate and said sacrificialassembly plate.
 11. The probe assembly of claim 9 wherein saidattachment face is opposite of said first fixture surface.
 12. The probeassembly of claim 9 wherein said sacrificial assembly plate comprises athird surface having a secondary positioning hole offset to said primarypositioning hole.
 13. The probe assembly of claim 12 wherein said thirdsurface comprises a surface offset to said first fixture surface in adirection of said primary positioning hole and said secondarypositioning hole.
 14. The probe assembly of claim 12 wherein said probecomprises a tip positioning pin disposed in said secondary positioninghole.
 15. The probe assembly of claim 14 wherein said first fixturesurface comprises an alignment hole and an orienting hole defining afirst positioning axis.
 16. The probe assembly of claim 15 wherein asecond alignment hole and a second orienting hole define a secondpositioning axis in a fan-out angle to said first positioning axis suchthat an alignment hole distance between said at least one alignment holeand said second alignment hole is substantially smaller than anorienting hole distance between said at least one orienting hole andsaid second orienting hole.
 17. The probe assembly of claim 15 whereinsaid alignment hole distance is about the same as said positioning holepitch.
 18. The probe assembly of claim 15 further comprising a fan-outbeam.
 19. The probe assembly of claim 18 wherein said fan-out beamcomprises a probe connect end and a peripheral connect end on a connectsurface.
 20. The probe assembly of claim 19 wherein said fan-out beamcomprises a beam attachment face opposite said connect surface.
 21. Theprobe assembly of claim 20 wherein said beam attachment face comprisesan elbow alignment pin in proximity to said probe connect end.
 22. Theprobe assembly of claim 21 wherein said elbow alignment pin is disposedin said alignment hole.
 23. The probe assembly of claim 19 furthercomprising conductive bridges to establish a conductive path betweensaid tip positioning pins and said peripheral connect ends.
 24. Theprobe assembly of claim 18 wherein said fan-out beam is disposed on saidfirst fixture surface.
 25. The probe assembly of claim 18 wherein saidfan-out beam further comprises an orienting pin.
 26. The probe assemblyof claim 25 wherein said orienting pin is disposed in said orientinghole of said first fixture surface.
 27. The probe assembly of claim 1wherein said second fixture surface extends in a substantially constantoffset in a direction of said primary positioning holes.
 28. The probeassembly of claim 1 wherein said primary positioning hole is linearlyarrayed.
 29. The probe assembly of claim 1 wherein said second surfaceis substantially planar.
 30. The probe assembly of claim 1 wherein saidfirst fixture plate is substantially perpendicular to said secondfixture surface.
 31. A layered probe for testing a device under testcomprising: an offset arm extending outwardly in a first direction; anelbow positioning pin extending from said offset arm; a suspensionstructure comprising one end at said offset arm and an opposing tip end,said opposing tip end comprising a tip positioning pin; said suspensionstructure extending downwardly from said offset arm in a seconddirection; said suspension structure further extending outwardly at saidtip end in substantially said first direction; and said layered probecomprising a center layer comprising said tip positioning pin interposedbetween outer layers.
 32. The probe of claim 31 further comprising anelbow between said offset arm and said suspension structure.
 33. Theprobe of claim 31 wherein said tip positioning pin is configured forinsertion in a tip pin hole along a contacting axis.
 34. The probe ofclaim 31 wherein said tip positioning pin comprises a rectangular crosssection.
 35. The probe of claim 31 wherein said tip positioning pincomprises a square cross section.
 36. The probe of claim 31 wherein saidelbow positioning pin is inserted in an elbow pin hole.
 37. The probe ofclaim 31 further comprising a fixed probe assembly, wherein said fixedprobe assembly comprises a fixture plate for holding a plurality ofprobes, said probe disposed on said fixture plate.
 38. The probe ofclaim 37 wherein said fixture plate comprises: a first fixture surfacecomprising a primary positioning hole arrayed with a positioning holepitch; and a second fixture surface in a substantially non-parallelfixture surface angle to said first fixture surface.
 39. The probe ofclaim 38 wherein said elbow positioning pin is disposed in said primarypositioning hole.
 40. The probe of claim 38 further comprising asacrificial assembly plate separably attached to an attachment face ofsaid fixture plate.
 41. The probe of claim 40 further comprising asacrificial spacing structure interposed between said probe fixtureplate and said sacrificial assembly plate.
 42. The probe of claim 40wherein said attachment face is opposite of said first fixture surface.43. The probe of claim 40 wherein said sacrificial assembly platecomprises a third surface having a secondary positioning hole offset tosaid primary positioning hole.
 44. The probe of claim 43 wherein saidthird surface comprises a surface offset to said first fixture surfacein a direction of said primary positioning hole and said secondarypositioning hole.
 45. The probe of claim 43 wherein said tip positioningpin disposed in said secondary positioning hole.
 46. The probe of claim45 wherein said first fixture surface comprises an alignment hole and anorienting hole defining a first positioning axis.
 47. The probe of claim46 wherein a second alignment hole and a second orienting hole define asecond positioning axis in a fan-out angle to said first positioningaxis such that an alignment hole distance between said at least onealignment hole and said second alignment hole is substantially smallerthan an orienting hole distance between said at least one orienting holeand said second orienting hole.
 48. The probe of claim 46 wherein saidalignment hole distance is about the same as a positioning hole pitch.49. The probe of claim 46 further comprising a fan-out beam.
 50. Theprobe of claim 49 wherein said fan-out beam comprises a probe connectend and a peripheral connect end on a connect surface.
 51. The probe ofclaim 50 wherein said fan-out beam comprises a beam attachment faceopposite said connect surface.
 52. The probe of claim 51 wherein saidbeam attachment face comprises an elbow alignment pin in proximity tosaid probe connect end.
 53. The probe of claim 52 wherein said elbowalignment pin is disposed in said alignment hole.
 54. The probe of claim50 further comprising conductive bridges to establish a conductive pathbetween said tip positioning pins and said peripheral connect ends. 55.The probe of claim 49 wherein said fan-out beam is disposed on saidfirst fixture surface.
 56. The probe of claim 49 wherein said fan-outbeam further comprises an orienting pin.
 57. The probe of claim 56wherein said orienting pin is disposed in said orienting hole of saidfirst fixture surface.
 58. The probe of claim 38 wherein said secondfixture surface extends in a substantially constant offset in adirection of said primary positioning holes.
 59. The probe of claim 38wherein said primary positioning hole is linearly arrayed.
 60. The probeof claim 38 wherein said second surface is substantially planar.
 61. Theprobe of claim 38 wherein said first fixture plate is substantiallyperpendicular to said second fixture surface.
 62. The probe of claim 31wherein said offset arm is substantially rigid.
 63. The probe of claim62 wherein said suspension structure and tip end are substantiallyrigid.
 64. The probe of claim 31 wherein said probe is substantiallysymmetric about a symmetry plane.
 65. The probe of claim 31 wherein saidsuspension structure comprises a cantilever.
 66. The probe of claim 31wherein said suspension structure comprises a knee suspension.
 67. Theprobe of claim 31 wherein said suspension structure comprises a bend.68. The probe of claim 31 wherein said first direction is substantiallyhorizontal.
 69. The probe of claim 31 wherein said second direction issubstantially vertical.
 70. The probe of claim 31 wherein said tippositioning pin is discrete from said opposing tip end.